1. Field of the Invention
The present invention relates to a thin film transistor-liquid crystal display (hereinafter referred to as a TFT-LCD) and a manufacturing method of the same.
2. Description of the Related Art
A conventional TFT-LCD consists of a gate electrode, an insulating layer, a semiconductor layer, a source/drain electrode, a passivation layer, and a pixel electrode layer.
Amorphous silicon is generally used as the semiconductor layer. The amorphous silicon has a mobility in the range of 0.5-1.0 cm.sup.2 /Vsec!. However, the mobility of the amorphous silicon is too low to drive a TFT, since the mobility needed for driving a TFT is 50-150 cm.sup.2 /Vsec!.
Therefore, a TFT using amorphous silicon must have a driving IC outside of a liquid crystal panel to drive the TFT. But using a driving IC is troublesome. Accordingly, it would be preferable for TFTs to use a semiconductor layer made from poly silicon, which has a high mobility of around 50-150 m.sup.2 /Vsec!.
A poly silicon TFT preferably has grains that are large. It is also desirable that the grains and the space between the grains do not have defects, and that the surface has minimal roughness.
In attempting to obtain these characteristics, fabrication sequences for semiconductor layer of a conventional poly silicon TFT-LCD will now be described.
FIGS. 1A-2E show cross-sectional views of a fabrication sequence for a conventional poly silicon TFT-LCD.
FIG. 1A illustrates a substrate 102. FIG. 1B illustrates depositing an amorphous silicon 104 on the substrate 102. FIG. 1C shows annealing the amorphous silicon with a temperature in the range of 500.degree.-700.degree. C. to transform the amorphous silicon 104 to a poly silicon 106 having increased grain size. FIG. 1D illustrates patterning the poly silicon 106 to obtain a patterned layer 106A.
Annealing of the patterned poly silicon 106A is illustrated in FIG. 1E, with a temperature in the range of 800.degree.-1100.degree. C. to obtain patterned poly silicon layer 106B having improved crystallization characteristics.
FIGS. 2A-2F show cross-sectional views of another fabrication sequence for a conventional poly silicon TFT-LCD.
FIG. 2A illustrates a substrate 202, on which there is deposited an amorphous silicon 204, as shown in FIG. 2B. FIG. 2C illustrates depositing a photoresist 205, patterning the photoresist 205, and implanting ions in the amorphous silicon 204. FIG. 2D illustrates annealing the amorphous silicon 204 with a temperature in the range of 500.degree.-700.degree. C. to transform the amorphous silicon 204 to a poly silicon 206 having increased grain size.
FIG. 2E illustrates patterning the poly silicon 206 to obtain a patterned layer 206A, which is then further annealed as illustrated in FIG. 2F with a temperature in the range of 800.degree.-1100.degree. C. to obtain patterned poly silicon 206B having improved crystallization characteristics.
FIGS. 3A-3D show cross-sectional views of another fabrication sequence for a conventional poly silicon TFT-LCD.
FIG. 3A illustrates a substrate 302, on which there is deposited a poly silicon 306, as shown in FIG. 3B. FIG. 3C illustrates implanting ions in the poly silicon 306 and annealing the poly silicon 306 with a temperature in the range of 500.degree.-700.degree. C. FIG. 3D illustrates patterning a poly silicon 306 to obtain a patterned layer 306A.
The above-described conventional poly TFT-LCD is not perfectly crystallized, therefore, additional time is needed for heating and annealing.